Another law suit filed against Citigroup, this one on behalf of participants in its 401(k) plans, alleging that the plan invested a significant amount of its funds into Citigroup stock -- about 32% of the plans' assets as of December 2006. According to plaintiffs, this investment policy violated federal pension law and the prudent investor rule and exposed the plan participants to excessive risk. CFO.com, Citigroup Slapped with 401(k) Suit.